1. Field of the Invention
The present invention relates to vehicle suspension and more specifically to a leaf spring type suspension for use on road vehicles.
2. Description of the Prior Art and Related Information
Whilst coil spring suspension systems are adopted for a number of modern passenger vehicles, leaf spring suspension systems are often preferred for vehicles which are capable of supporting greater loads, such as, for example vans, trucks, buses, trailers and other passenger or commercial vehicles.
A conventional leaf spring arrangement is typically attached at its opposing ends to a chassis member via intermediate links referred to as hangers. The vehicle axle is attached to a central portion of the leaf spring arrangement such that relative movement between the axle and the chassis member is resisted by the restoring force of the leaf spring.
A conventional multi-leaf or parabolic leaf spring suspension systems provides for a fixed vehicle ride height under steady state loading conditions. However there are a number of practical reasons why it may be necessary to raise or lower the vehicle height relative to the axle. Such instances include, for example, the carrying heavy loads, for towing trailers or the like, or the lowering of suspension for improved vehicle handling. These adjustments would generally require a conventional leaf spring suspension system to be removed and modified or replaced with an alternative leaf spring arrangement in order to allow a different height to be achieved.
It will be appreciated by those skilled in the art that the adjustment or replacement of such conventional leaf spring suspension systems requires a considerable amount of work and is not readily undertaken without a specific commercial need. The replacement of a leaf spring suspension system can result in a vehicle being off the road for a number of days, which is particularly undesirable for commercial vehicles.
This problem has been acknowledged and a number of solutions have been proposed in the past. One such solution involves the use of a tensioning arrangement, typically in the form of a hydraulic piston and cylinder, which can raise and lower the height of the chassis relative to the axle against the force of the spring. However this solution significantly increases the cost and complexity of the suspension system and compromises the effectiveness of the leaf spring arrangement by forcing it to operate in a condition which is offset from the natural equilibrium of the spring.
The adjustment of a leaf spring suspension to allow the chassis to be raised or lowered relative to the axle poses a particular design problem since a conventional leaf spring suspension system also serves a secondary function in that it maintains the lateral stability of the chassis relative to the axle.
It is an object of the present invention to provide an improved vehicle suspension system which allows adjustment of the height of chassis relative to the axle without substantially jeopardizing the lateral stability of the vehicle. It is a further object of the present invention to provide a suspension system which is simple to install and adjust.